Most horopter data are suspect because eye movements have not been accounted for. This is particularly critical for data involving fusional stimuli, as can be created by prism, vergence lenses, and size lenses, in normal subjects. It is the purpose of this study to determine horopter shape and location under conditions of induced fusional stimuli. Because such stresses occur in patients with fixation disparity, heterophoria, aniseikonia and anomalous correspondence, this study should shed light on the binocular relationship known as corresponding points under such circumstances. It is hypothesized that some sensory-motor interactions will be revealed by a shift, transient, or more lasting of the horopter locus under such conditions. Horopters will be measured with and without appliances that induce a small load on the fusional mechanism. These appliances will be worn steadily during determinations, or introduced for short periods of time. Eye movements will be monitored so that findings obtained during overt movement of the eyes may be eliminated from further analysis. Analysis will be accomplished by determining the mean settings and mean deviations of points sampling the binocular visual field between 12 degrees-left and 12 degrees-right. These will be expressed in binocular disparity. The binocular nonius and classical nonius criterion will be compared and the horopter in anomalous correspondence will be dtermined. Furthermore, some simplified methods suitable for clinical use will be explored, following attempts to establish optimum neutralization of the sensory-motor effects of heterophoria, fixation disparity, and aniseikonia.